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If you've still got battery smoke alarms dotted round the ceiling, I'll be straight with you: they're not doing what you think they're doing. Batteries get taken out because they're beeping at 3am. Units go past their sell-by date and nobody notices. And if the worst happens, your insurer will ask whether you had working, correctly located, in-date detectors — not whether you meant to replace them.
I've been fitting these for 25 years across Tonbridge, Tunbridge Wells, Sevenoaks and Crowborough, and I'll give you straight 2026 pricing, where each alarm type actually needs to go, and why this one isn't a job to have a go at yourself.
If you've already got wired alarms, replacing like-for-like in the same positions is the cheapest and simplest route.
Both plus VAT, plus a separate disposal charge for taking the old units away properly.
That price includes a new alarm with a built-in 10-year battery, fitting into your existing wired position, an interlink check so all alarms sound together, and a rundown of when it'll need replacing.
Heat alarms go in kitchens, garages and utility rooms — anywhere smoke alarms would be triggered constantly by cooking steam or fumes rather than an actual fire. They respond to a rapid temperature rise, not particles in the air.
If you're having one fitted alongside smoke or CO alarms, I'll quote the whole job as one fitted price so you know the total upfront.
CO is colourless, odourless, and kills quickly. Anywhere fossil fuel is burned — gas boilers, wood-burners, coal fires, gas water heaters — needs a CO alarm.
Positioning matters here. CO disperses evenly through a room rather than rising like smoke, so alarms usually go at breathing height on a wall or on the ceiling, depending on the manufacturer's instructions and the room layout.
In a kitchen with a gas hob, or a compact boiler room, a combined unit covering both heat and CO can be the better call — one device instead of two.
Old alarms are electrical waste under WEEE regulations, and some contain components that need careful handling. Every quote includes collecting your old units and disposing of them properly — it's not an add-on I've bolted on to pad the invoice, it's how they legally have to be dealt with.
A properly protected home doesn't rely on one type of detector doing everything. Each one has a specific job:
Smoke alarms — hallways and landings, particularly between bedrooms and escape routes, main living areas, and anywhere with a solar PV inverter or battery storage system. Inverters and battery packs can, in rare fault conditions, overheat — a smoke alarm in that room gives you early warning before it becomes visible elsewhere. Fit on the ceiling, at least 300mm from walls and light fittings, and interlinked so one going off sets all of them off.
Heat alarms — kitchens and garages, ceiling mounted, positioned away from the cooker itself but within the same room.
CO alarms — any room or loft space with a gas boiler, living rooms with wood-burners or open fires, anywhere with a flued or fuel-burning appliance.
Combined heat & CO alarms — kitchens with gas appliances, boiler rooms, or anywhere space is tight and you want one device covering two risks.
Every modern alarm — smoke, heat or CO — is designed around a 10-year working life, and that applies to both the sensor and the built-in battery.
Smoke sensors pick up dust and airborne particles over time and get slower to react. Heat sensors go through thousands of thermal cycles and can drift out of calibration. CO sensors chemically age, which reduces their accuracy. That's why decent alarms have a "replace by" date printed on the case — once you're past it, the unit is no longer within its certified working life, whatever it looks like on the ceiling.
The built-in battery in mains alarms is usually a sealed lithium cell with the same 10-year design life as the sensor. You can't just swap the battery — when it's due, the whole unit gets replaced. If yours starts chirping intermittently or shows a fault light, that's it telling you it's done.
Yes, and this is the bit most homeowners don't know until it's too late.
If you have a fire and your alarms are clearly past their 10-year mark, or weren't working at the time, that gets noted in the fire investigator's report. Insurers can and do use that to argue you didn't take reasonable safety precautions — and reduce your payout, or in serious cases refuse it outright.
The same applies to old battery-only alarms with the battery removed or dead. If there's no working alarm where there reasonably should have been one, you're looking at the same risk. This is exactly why I push people toward mains-powered, interlinked systems with CO and heat cover where it's needed, kept within their 10-year life.
I wouldn't, and here's why. When you take one of these down, you'll typically find six or more wires behind it — permanent live, neutral, an interlink wire to other alarms, earth, and often a loop-through feed to another part of the circuit. The back box is frequently acting as a junction point for more than just that one alarm.
Get a conductor wrong — mix up the interlink wire with a live, leave an earth loose, assume the colours match modern standards when they don't — and you can disable other alarms in the house, introduce a shock risk, trip breakers, or in the worst case create a fire risk of your own making.
There's also a compatibility issue: not every brand talks to every other brand's interlink system. Swap in a different manufacturer without checking, and your alarms might stop triggering each other altogether. Any electrician doing this properly will identify your existing wiring method, supply compatible units, test that everything sounds together, and carry out the work to BS 7671 and current Building Regulations — including Part P where it applies.
Put together properly, a well-protected home usually has:
Smoke alarms in hallways and landings on every floor, the main living area, and any room with solar PV or battery storage. Heat alarms in the kitchen and garage. CO alarms anywhere with a gas boiler or an open fire. Combined heat & CO units in kitchens with gas appliances or compact plant rooms.
Mains-powered, interlinked, and within their 10-year life, that combination gives you early warning of fire, early warning of dangerous CO, and a much stronger position if you ever need to make an insurance claim.
We check the age and "replace by" date on every existing alarm, confirm they're in the right locations, and test interlinking and basic function. You get clear, itemised pricing before anything's fitted — no surprises on the invoice. Once installed, we test every alarm in front of you and talk you through monthly testing, what the warning chirps mean, and when to expect the next replacement.
If you're in or around Tonbridge, Tunbridge Wells, Sevenoaks or Crowborough and your alarms are approaching or past 10 years old, don't wait for an incident to find out they're not compliant. It's a modest job that makes a real difference when it counts.
Call 01892 531 728, WhatsApp 07775 561 363, or email karen@brightsparkelectrician.co.uk.
After moving house I had a lot of electrical work needed doing. Bright Sparks made a very good job of it all and has left me confident in the electrics in the house. The work consisted of a new fuse box, new lights, switches and plugs etc. The work was carried out in a clean, pleasant manner. I would definitely recommend this company. Margaret C
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Karen and her team of electricians are super responsive, very professional, and I love how they book an exact time and appointment with a follow-up confirmation text and email. I feel very confident in the quality of workmanship and know they will go out of their way to fix any electrical issues in my home!
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You just saved us the biggest headache ever; after months of electrical problems ( now resolved), we had a ‘no power situation’. After checking circuit boards, switches etc we were at a complete loss. Read your piece above (after Googling ‘circuit board switches up, but no power‘) about RCD switch and resetting (didn’t know what an RCD was), and after 8 hours sleep dreaming of circuit boards and 2 minutes of contemplation, and re-reading your advice,I totally nailed it. Brilliant tutorial, many thanks. Susanne (I am neither young nor savvy with anything technical)
